Parking brake assembly with wear adjustment for heavy road vehicle disc brake

ABSTRACT

In a disc brake ( 10 ) having a disc ( 16 ) and a brake shoe ( 82 ) movable towards and away from a friction surface ( 86 ) provided on one face of the disc ( 16 ), there is provided a parking brake ( 22   a   /22   b ) having a pushing member ( 44   a   /44   b ) for moving the brake shoe ( 82 ) towards and away from the friction surface ( 86 ) of the disc ( 16 ). The parking brake ( 22   a   /22   b ) further includes a cam ( 36   a   /36   b ) displaceable between a first position in which the cam ( 36   a   /36   b ) forces the pushing member ( 44   a   /44   b ) against a biasing force acting thereon to maintain the brake shoe ( 82 ) in friction engagement with the disc ( 16 ) and a second position in which the pushing member ( 44   a   /44   b ) is free to move in a direction away from the disc ( 16 ) to release the brake shoe ( 82 ) from the friction surface ( 86 ) of the disc ( 16 ). A piston and cylinder arrangement ( 28 ) is provided to displace the cam ( 36   a   /36   b ) between its first and second positions.

RELATED APPLICATIONS

[0001] This is a continuation of International Patent Application No.PCT/CA01/01448 filed Oct. 18, 2001, which claims benefit of CanadianPatent Application No. 2,323,817 filed on Oct. 18, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a vehicle brake system and, moreparticularly, to disc brakes for heavy road vehicles.

[0004] 2. Description of the Prior Art

[0005] U.S. Pat. No. 5,205,380 issued to Paquet et al. on Apr. 27, 1993discloses a disc brake assembly for heavy road vehicles. The disc brakeassembly includes a parking or safety brake which is automaticallyactivated when the road vehicle is parked. The parking brake comprisesspring acting on a movable plate to urge a brake shoe against a frictionsurface provided on one face of a disc. A fluid bladder is provided toovercome, when expanded, the force of the spring in order to release thebrake shoe from the friction surface of the disc.

[0006] Although the parking brake described in the above-mentionedpatent is effective, it has been found that there is a need for a newparking brake which is more compact.

SUMMARY OF THE INVENTION

[0007] It is an aim of the present invention to provide a new parkingbrake for a disc brake assembly.

[0008] It is also an aim of the present invention to provide a new discbrake assembly having a system for automatically repositioning a brakeshoe to compensate for wear thereof.

[0009] It is a further aim of the present invention to provide a compactparking brake which is integrated with a disc brake assembly.

[0010] Therefore, in accordance with the present invention, there isprovided a disc brake assembly having a disc and a brake shoe movabletowards and away from a friction surface provided on one face of thedisc, and a parking brake comprising a first pushing member for movingthe brake shoe towards and away from the friction surface of the disc, afirst movement transmitting member displaceable between a first positionwherein said first movement transmitting member forces said firstpushing member against a biasing force acting thereon to maintain thebrake shoe in friction engagement with the disc and a second positionwherein said first pushing member is free to move in a direction awayfrom the disc to release the brake shoe from the friction surface of thedisc, and a motive means to displace said first movement transmittingmember between said first and second positions thereof.

[0011] In accordance with a further general aspect of the presentinvention, there is provided a parking brake for mechanical connectionto a wheel of a vehicle for maintaining the vehicle stationary,comprising a disc adapted to be mounted to the wheel and having afriction surface on a face thereof, a brake shoe movable towards andaway from said friction surface of said disc, and a brake actuator fornormally maintaining said brake shoe against said friction surface, saidbrake actuator comprising a first pushing member biased in a directionaway from said friction surface, said brake shoe being movable by saidfirst pushing member, and a first cam displaceable by a motive meansbetween a first position wherein said first pushing member is pushedagainst a biasing force thereof by said first cam and a second positionwherein said first pushing member is allowed to return to a restposition thereof under the biasing force acting thereon, and whereinsaid brake shoe is applied against said friction surface as long as saidfirst pushing member is pushed by said first cam against said biasingforce thereof.

[0012] In accordance with a further general aspect of the presentinvention, there is provided a self-adjusting brake for a wheel on avehicle, comprising at least one disc adapted to be mounted to the wheeland having a friction surface on one face thereof, at least one brakeshoe movable axially towards and away from said friction surface forfriction engagement therewith and release thereof, and a brake actuatorfor displacing the brake shoe from an idle position to a functionalposition in which said brake shoe is urged against said friction surfaceof said disc, a wear compensating mechanism for automaticallyreadjusting said idle position of said brake shoe to accommodate wearthereof, at least two pivotally mounted ratchet arms biased towards aclosed position wherein said ratchet arms are urged in toothedengagement with a pawl member, said ratchet arms having a number ofaxially spaced-apart level of notches, said pawl member being looselymounted for limited axial movement along an axially extending brake shoeprojection so that when the stroke of the brake shoe becomes greaterthan a permitted distance of travel of said pawl member on said brakeshoe projection, said ratchet arms are pivoted to an open positionthereof by said pawl member to allow said pawl member to fall into anext level of notches on said ratchet) arms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Having thus generally described the nature of the invention,reference will now be made to the accompanying drawings, showing by wayof illustration a preferred embodiment thereof, and in which:

[0014]FIG. 1 is a top view of a disc brake assembly for heavy roadvehicles in accordance with a first embodiment of the present invention;

[0015]FIG. 2 is a rear plan view of the disc brake assembly of FIG. 1;

[0016]FIG. 3 is an enlarged perspective view, partly in section, of thedisc brake assembly illustrated in an idle position thereof;

[0017]FIG. 4 is an enlarged cross-sectional view of a parking brakespring biased in an idle position thereof; and

[0018]FIG. 5 is an exploded perspective view of a pair of parking brakeforming part of the disc brake assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Now referring to the drawings, an in particular to FIGS. 1 and 3,a disc brake assembly 10 suited for heavy road vehicles, such as trucks,busses, tractors or trailers, will be described.

[0020] As illustrated in FIG. 1, the disc brake assembly 10 comprises ahousing 12 adapted to be mounted on an axle 14 of a vehicle for housinga pair of axially spaced-apart ventilated discs 16 and 18 adapted to beconnected to the hub 20 of a wheel (not shown) for rotative movementtherewith, as described in U.S. Pat. No. 5,205,380 issued on Apr. 27,1993 to Paquet et al.

[0021] A pair of mechanically linked identical parking brakes 22 a, 22 bare housed in respective cylindrical shells 24 a and 24 b secured onopposed sides of the housing 12. The security or parking brakes 22 a and22 b are mechanically connected with a disc brake sub-assembly 26 (FIG.3) which is, in turn, operatively connected to the pedal brake (notshown) of the vehicle to act as the main brake of the vehicle to controlthe speed thereof when the latter is in operation.

[0022] As shown in FIG. 2, the parking brakes 22 a and 22 b aremechanically linked and operated by a brake actuator including apneumatic cylinder 28 extending therebetween. The pneumatic cylinder 28includes a cylindrical housing 30 and a piston rod 32 normally biased ina retracted position by a spring (not shown) provided within thecylindrical housing 30. As shown in FIG. 5, the piston rod 32 ispivotally connected at 34 to a cam 36 a which is, in turn, pivotallymounted at 35 to a bracket 38 a secured onto the shell 24 a. Likewise,the housing 30 is pivotally mounted at 40 to a cam 36 b which is, inturn, pivotally mounted to a bracket 38 b secured onto the shell 24 b.Therefore, when the biasing force of the spring (not shown) of thepneumatic cylinder 28 is overcome by the air pressure directed into thehousing 30 via conventional fluid lines (not shown), the piston rod 32will slide axially out of the housing 30 to an extended positionthereof, thereby causing the cams 36 a and 36 b to rotate in opposeddirections, as depicted by arrows 39 a and 39 b in FIG. 1, respectively.As seen in FIG. 5, a brace member 42 extends between the brackets 38 aand 38 b to structurally unify the same and increase the rigidity of theassembly. The brackets 38 a and 38 b have respective bottom through bore41 a and 41 b for receiving corresponding tubular necks 43 a and 43 bformed on respective top surfaces of the shells 24 a and 24 b. The termcam is herein intended to encompass any rotating or sliding piece of anydefinite shape for imparting a desired movement to the pushing members44 a and 44 b. For instance, a sliding wedge defining an inclinedsurface could also be used to displace the pushing members 44 a and 44b. It is also contemplated to use a pantograph linkage or a pair ofscissor links in lieu of a cam to transmit a movement to the pushingmembers 44 a and 44 b.

[0023] Referring now to FIG. 4, the action of the cam 36 b on theparking brake 22 b, as well as the structural details of the latter willnow be described. The interaction between the cam 36 a and the parkingbrake 22 a is similar to that of the cam 36 b and the parking brake 22 band, thus, the duplicate description thereof will be omitted. Thestructural details of the parking brake 22 a, which are identical tothose of the parking brake 22 b, will not be repeated for brevity.

[0024] As seen in FIG. 4, the parking brake 22 b includes a pushingmember 44 b mounted for axial movement within the shell 24 b and havinga cylindrical stem portion 46 b extending outwardly of the shell 24 bthrough a cylindrical passage 48 b defined by the tubular neck 43 bthereof. The cam 36 b has a curved cam surface 50 b for engaging adomed-shaped terminal distal end 52 b of the cylindrical stem portion 46b. Upon rotation of the cam 36 b in the direction indicated by arrow 54,the pushing member 44 b will be pushed axially into the shell 24 b dueto the curvature of the cam surface 50 b.

[0025] The pushing member 44 b has three circumferentially spaced-apartratchet arms 55 b, 57 b, 59 b (FIG. 5) pivotally mounted thereto forengagement with a pawl provided in the form of an annular ring 61 bloosely fitted about a piston head 56 b securely mounted to aspring-loaded pusher or piston 58 b. More particularly, the annular ring61 b has a beveled bottom rim 63 b for mating engagement into axiallyspaced-apart interdental spaces or notches 65 b defined on respectiveinner surfaces of the ratchet arms 55 b, 57 b and 59 b. The ratchet arms55 b, 57 b and 59 b are normally biased radially inwardly to a closedposition thereof against the annular ring 61 b by an annular springmember 66 b encircling the lower ends of the arms 55 b, 57 b and 59 b.The piston 58 b has a stem 68 b having a radially enlarged end portion70 b from the periphery of which depends a cylindrical skirt 72 bdefining an annular seat 74 b about the stem 68 b for receiving one endof a compression spring 76 b. The other end of the spring 76 b isabutted against a spider 77 b mounted on the axle 14 to support thehousing 12 and receive the actuator of the disc brake-sub-assembly 26.An annular dish member 78 b extends about the skirt 72 b and is urgedagainst the free terminal ends of the arms 55 b, 57 b and 59 b by asecond compression spring 80 b concentrically disposed about the firstspring 76 b and having a first end abutting against the dish member 78 band a second opposed end received in an annular seat 79 b defined in thespider 77 b. The second spring 80 b normally urges the dish member 78 bagainst the arms 55 b, 57 b and 59 b to resist the axial displacement ofthe pushing member 44 b and, thus, allow the radial deployment of thearms 55 b, 57 b and 59 b when the piston 58 b is drawn against thespring 76 a in response to the activation of the disc brake sub-assembly26 to brake or control the speed of the vehicle, as will be explainedhereinafter.

[0026] The piston 58 a and 58 b are structurally connected to an annularpressure plate 82 (see FIG. 3) by conventional fastening elements (notshown). Therefore, the axial displacement imparted to the pushingmembers 44 a and 44 b by the rotational movement of the cams 36 a and 36b and transferred from the pushing members 44 a and 44 b to the pistons58 a and 58 b via the ratchet arms 55 a, 55 b, 57 a, 57 b, 59 a, 59 band the annular rings 61 a and 61 b, will be communicated to thepressure plate 82 which forms part of the main brake, herein referred toas the disc brake sub-assembly 26.

[0027] As seen in FIG. 3, a plurality of brake shoe lining segments 84forming a lining ring or, alternatively, a one-piece lining ring are/ismounted to the front surface of the pressure plate 82 adjacent a radialfriction surface 86 of the disc 16. A second brake shoe lining ring 88is mounted to an axially movable intermediate annular plate 90 adjacenta second radial friction surface 92 of the disc 16 opposite the firstfriction surface 86 thereof. The intermediate plate 90 is slidablymounted to the pressure plate 82. As seen in FIG. 3, the intermediateplate 90 includes a plurality of axially extending fingers 94 which areslidably receive in corresponding channels 96 formed on an axiallyextending portion of the pressure plate 82. A third brake shoe lining 98(FIG. 1) is mounted to the intermediate plate 90 opposite the secondbrake shoe lining 88 adjacent a radial friction surface (not shown) ofthe second disc 18. A fourth stationary brake lining (not shown) ismounted within the housing 12 adjacent a second friction surface (notshown) of the second disc 18 opposite the first friction surfacethereof.

[0028] When the vehicle is not in operation, the pneumatic cylinder 28is depressurized so as to retract the piston rod 32 and cause therotation of the cams 36 a and 36 b in the direction indicated by arrows39 a and 39 b in FIG. 1. The rotational movement of the cams 36 a and 36b will cause the pushing members 44 a and 44 b to be pushed withinrespective shells 24 a and 24 b, thereby pushing the pistons 58 a and 58b and the annular dish members 78 a and 78 b against the springs 76 a,76 b and 80 a, 80 b, respectively. The pistons 58 a and 58 b will thenpush on the pressure plate 82 which will, in turn, press the movablebrake shoe lining 84 against the friction surface 86 of the first disc16 which is mounted for limited axial movement on the axle 14 via aspline arrangement (not shown), as described in U.S. Pat. No. 5,205,380issued to Paquet et al. Therefore, the first disc 16 will also be pushedagainst the second brake shoe lining 88 which will, in turn, push theintermediate plate 90, and the third brake shoe lining 98 against thesecond disc 18 which will move axially against the stationary brake shoelining (not shown).

[0029] When the pneumatic cylinder 28 is pressurized, the springs 76 aand 76 b act on the pistons 58 a and 58 b to maintain the brake shoelinings 84, 88 and 98 out of engagement with the discs 16 and 18,thereby allowing the discs 16 and 18 to rotate freely with theassociated wheel (not shown).

[0030] When the vehicle is operated, the parking brakes 22 a and 22 bare disabled, i.e. the pneumatic cylinder 28 is pressurized, and thespeed of the vehicle is controlled by a pneumatic brake actuator 100(FIG. 3) mounted within the spider 77 b for selectively pushing thepressure plate 82 towards the discs 16 and 18 to engage the movablebrake shoe linings 84, 88 and 98 and the stationary brake shoe lining(not shown) with the radial friction surfaces of the discs 16 and 18, asdescribed hereinbefore with respect to the parking brakes 22 a and 22 b.As the pressure plate 82 is pushed by the pneumatic brake actuator 100,the pistons 58 a and 58 b are pulled against the springs 76 a and 76 bthereof. As seen in FIG. 4, the piston head 56 b has a flange 102 bwhich is axially spaced from the annular ring 61 b to define therewith aplay 104 b when the piston 58 b is at rest, i.e. when the piston 58 b isnot solicited by external axial forces. It is understood that a similarplay exist between the piston head 56 a and the annular ring 61 a. Theseplays correspond to the play existing between the brake shoe linings 84,88 and 98 and the discs 16 and 18 when the brake assembly 10 is notoperated and the discs 16 and 18 are free to rotate.

[0031] Therefore, when the pneumatic actuator 100 is activated todisplace the pressure plate 82, the pistons 58 a and 58 b will travelwith the pressure plate 82 over an axial distance corresponding to theplay 104 b. Accordingly, the annular rings 61 a and 61 b will remaintrapped in the first level of notches 65 a and 65 b. However, when thebrake shoe linings 84, 88 and 98 will become worn, the thickness thereofwill reduce and consequently the displacement of the pressure plate 82and the pistons 58 a and 58 b necessary to effect braking will increase.At a certain level of wear of the brake shoe linings 84, 88 and 98, thedisplacement of the pressure plate 82 and the pistons 58 a and 58 bunder the governed of the pneumatic operator 100 will be such that theannular rings 61 a and 61 b will be drawn by the piston heads 56 a and56 b, thereby causing the radial deployment of the arms 55 a, 55 b, 57a, 57 b, 59 a and 59 b which are retained against axial movement by thespring loaded dish members 78 and 78 b, to allow the annular rings 61 aand 61 b to move axially relative to the arms 55 a, 55 b, 57 a, 57 b, 59a and 59 b beyond the first level of notches 65 a and 65 b thereof. Whenthe pressure exerted by the pneumatic actuator 100 is released, thesprings 76 a and 76 b will urge the pistons 58 a and 58 b and theannular rings 61 a and 61 b towards their original position but therespective beveled rims 63 a and 63 b of the annular rings 61 a and 61 bwill fall into the second level of notches 65 a and 65 b of the arms 55a, 55 b, 57 a, 57 b, 59 a and 59 b, which tend to return to theiroriginal closed position under the biasing force of the annular spring66 a and 66 b, thereby preventing the pistons 58 a and 58 b fromreturning to their original resting

[0032] When the brake shoe linings 84, 88 and 98 will become furtherworn, the annular rings 61 and 61 b will automatically fall in the nextlevel of notches 65 a and 65 b and so on. This mechanism allows toautomatically compensating for the wear of the brake shoe linings 84, 88and 98 to maintain the original adjustment of the parking brakes 22 aand 22 b irrespectively of the condition of the brake shoe linings 84,88 and 98.

1. In a disc brake assembly having a disc and a brake shoe movabletowards and away from a friction surface provided on one face of thedisc, a parking brake comprising a first pushing member for moving thebrake shoe towards and away from the friction surface of the disc, afirst movement transmitting member displaceable between a first positionwherein said first movement transmitting member forces said firstpushing member against a biasing force acting thereon to maintain thebrake shoe in friction engagement with the disc and a second positionwherein said first pushing member is free to move in a direction awayfrom the disc to release the brake shoe from the friction surface of thedisc, and a motive means to displace said first movement transmittingmember between said first and second positions thereof.
 2. A parkingbrake as defined in claim 1, wherein said first movement transmittingmember includes a first cam having a cam surface engaged with a freedistal end of said first pushing member.
 3. A parking brake as definedin claim 2, wherein said motive means includes a piston and cylinderarrangement, and wherein said first cam is pivoted at one end thereof tosaid piston and cylinder arrangement and at a second opposite endthereof to a fixed support structure.
 4. A parking brake as defined inclaim 3, further comprising a second cam and a second pushing member,said piston and cylinder arrangement being connected at one end thereofopposite said first cam to said second cam to displace said second camto a first position thereof in order to force said second pushing memberagainst a biasing force acting thereon to maintain the brake shoe infrictional engagement with the disc.
 5. A parking brake as defined inclaim 4, wherein said cylinder and piston arrangement has a housing anda piston rod, said first and second cams being respectively pivotallyconnected to said housing and said piston rod to cause said cam torotate in opposed directions upon axial movement of said piston rodrelative to said housing.
 6. A parking brake as defined in claim 5,wherein said piston rod is normally biased in a retracted position tomaintain said first and second cams in respective first positionsthereof so that said brake shoe be forced against the disc by said firstand second pushing members.
 7. A parking brake as defined in claim 3,wherein said piston and cylinder arrangement extends in a directiongenerally perpendicular to a direction of motion of said first pushingmember, and wherein said first cam has a pivot axis perpendicular tosaid piston and cylinder arrangement.
 8. A parking brake as defined inclaim 1, wherein at least two ratchet arms are pivotally mounted to saidfirst pushing member and biased towards a closed position wherein saidratchet arms are urged in toothed engagement with a pawl member, saidratchet arms having a number of axially spaced-apart level of notches,said pawl member being loosely mounted for limited axial movement alongan axially extending brake shoe projection so that when the stroke ofthe brake shoe becomes greater than a permitted distance of travel ofsaid pawl member on said brake shoe projection, said ratchet arms arepivoted to an open position thereof by said pawl member to allow saidpawl member to fall into a next level of notches on said ratchet arms inorder to compensate wear of said brake shoe.
 9. A parking brake asdefined in claim 8, wherein said brake shoe projection is biased in adirection away from said disc.
 10. A parking brake as defined in claim9, wherein said brake shoe projection is biased by a return spring. 11.A parking brake as defined in claim 8, further comprising a biasingmember to prevent said first pushing member from being drawn by saidbrake shoe projection under normal brake mode operation.
 12. A parkingbrake as defined in claim 11, wherein said biasing member is provided inthe form of a spring-loaded dish member.
 13. A parking brake formechanical connection to a wheel of a vehicle for maintaining thevehicle stationary, comprising a disc adapted to be mounted to the wheeland having a friction surface on a face thereof, a brake shoe movabletowards and away from said friction surface of said disc, and a brakeactuator for normally maintaining said brake shoe against said frictionsurface, said brake actuator comprising a first pushing member biased ina direction away from said friction surface, said brake shoe beingmovable by said first pushing member, and a first cam displaceable by amotive means between a first position wherein said first pushing memberis pushed against a biasing force thereof by said first cam and a secondposition wherein said first pushing member is allowed to return to arest position thereof under the biasing force acting thereon, andwherein said brake shoe is applied against said friction surface as longas said first pushing member is pushed by said first cam against saidbiasing force thereof.
 14. A parking brake as defined in claim 13,wherein said first cam has a cam surface engaged with a free distal endof said first pushing member.
 15. A parking brake as defined in claim14, wherein said motive means includes a piston and cylinderarrangement, and wherein said first cam is pivoted at one end thereof tosaid piston and cylinder arrangement and at a second opposite endthereof to a stationary bracket.
 16. A parking brake as defined in claim15, further comprising a second cam and a second pushing member, saidpiston and cylinder arrangement being connected at one end thereofopposite said first cam to said second cam to displace said second camin order to force said second pushing member against a biasing forceacting thereon to maintain the brake shoe in frictional engagement withthe disc.
 17. A parking brake as defined in claim 16, wherein saidcylinder and piston arrangement has a housing and a piston rod, saidfirst and second cams being respectively pivotally connected to saidhousing and said piston rod to cause said cam to rotate in opposeddirections upon axial movement of said piston rod relative to saidhousing.
 18. A parking brake as defined in claim 17, wherein said pistonrod is normally biased in a retracted position to cause said first andsecond cams to force said first and second pushing members
 19. A parkingbrake as defined in claim 13, wherein at least two ratchet arms arepivotally mounted to said first pushing member and biased towards aclosed position wherein said ratchet arms are urged in toothedengagement with a pawl member, said ratchet arms having a number ofaxially spaced-apart level of notches, said pawl member being looselymounted for limited axial movement along an axially extending brake shoeprojection so that when the stroke of the brake shoe becomes greaterthan a permitted distance of travel of said pawl member on said brakeshoe projection, said ratchet arms are pivoted to an open positionthereof by said pawl member to allow said pawl member to fall into anext level of notches on said ratchet arms in order to compensate wearof said brake shoe.
 20. A parking brake as defined-in claim 19, whereinsaid brake shoe projection is biased in a direction away from said disc.21. A parking brake as defined in claim 20, wherein said brake shoeprojection is biased by a return spring.
 22. A parking brake as definedin claim 19, further comprising a biasing member to prevent said firstpushing member from being drawn by said brake shoe projection undernormal brake mode operation.
 23. A parking brake as defined in claim 22,wherein said biasing member is provided in the form of a spring-loadeddish member.
 24. A self-adjusting brake for a wheel on a vehicle,comprising at least one disc adapted to be mounted to the wheel andhaving a friction surface on one face thereof, at least one brake shoemovable axially towards and away from said friction surface for frictionengagement therewith and release thereof, and a brake actuator fordisplacing the brake shoe from an idle position to a functional positionin which said brake shoe is urged against said friction surface of saiddisc, a wear compensating mechanism for automatically readjusting saididle position of said brake shoe to accommodate wear thereof, at leasttwo pivotally mounted ratchet arms biased towards a closed positionwherein said ratchet arms are urged in toothed engagement with a pawlmember, said ratchet arms having a number of axially spaced-apart levelof notches, said pawl member being loosely mounted for limited axialmovement along an axially extending brake shoe projection so that whenthe stroke of the brake shoe becomes greater than a permitted distanceof travel of said pawl member on said brake shoe projection, saidratchet arms are pivoted to an open position thereof by said pawl memberto allow said pawl member to fall into a next level of notches on saidratchet arms.